WRITING INSTRUMENT

摘要

The latent mark pen contains a latent ink prepared by admixing into 150ml water 2-10g phthalein group compd. selected from 2,4 dinitrophenol, phenolphthalein and thymolphthalein, 4-20g FeCl3 and ethylalcohol; the coloring pen contains a ink prepared admixing to 100ml water 1-5g NaCO3, 0.5-3.0g NaHCO3 and 3-8ml monoethanolamin. The user first makes a mark and then coats the coloring ink over the mark to bring up the latent mark in color.